The invention relates to an electronically controlled ignition system for internal combustion engines (hereinafter referred to as ESA).
Known ignition systems for internal combustion engines are so designed that an ignition coil thereof generates a high-energy output in order to control exhaust emissions and improve fuel consumption. Consequently, there is a disadvantage that, where the ignition coil is energized for a period of time corresponding to fixed degrees of the crankshaft rotation, if the degrees of crankshaft rotation corresponding to the required energizing period for rendering the ignition coil saturated with stored energy are set to fit a high engine speed, the energizing period will be increased excessively at lower speeds and consequently the energization of the ignition coil after the saturation of the stored energy will cause generation of heat in the ignition coil and the ignition coil drive circuit. On the other hand, the setting of the degrees of crankshaft rotation to fit a low engine speed raises a problem such that the energizing period will be decreased excessively at higher speeds and consequently there will not be saturation of stored energy of the ignition coil causing insufficient ignition energy.
Another type of ignition systems is known in the art in which a proper ignition coil energization starting timing is computed by a main computing unit and the ignition coil energizing period is controlled according to the computed data. However, this type of known ignition system has a disadvantage of requiring a pair of comparators, one for determining the time to energize the ignition coil and the other for determining the time to deenergize the ignition coil, which causes a complicated circuit construction.